Resin transfer molding device and resin transfer molding method

ABSTRACT

A resin transfer molding (RTM) molding device is designed to mold a fiber-reinforced plastic (FRP) molded body by injecting a resin composition into a mold and by impregnating the molded body therewith. The resin composition is a chain curing polymer (CCP). A CCP accommodating layer is disposed adjacent to an outer side of the molded body. The layer contains the CCP. The layer is provided with a Vf limit value, the value defined by the curing characteristics of the CCP and the characteristics of dissipation of heat from the CCP to the exterior. An element for separating the molded body is disposed between the body and the layer.

TECHNICAL FIELD

The present invention relates to a resin transfer molding (also referredto as “RTM” hereinafter) device and to an RTM molding method for use inmolding of a structure made of fiber-reinforced plastics (also referredto as “FRP” hereinafter). In particular, in the present invention, useof a CCP (resin composition of chain curing type) contributes to anincrease in the fiber volume content (also referred to as “Vf”hereinafter) of a FRP body to be molded. This results in the FRP bodyhaving superior strength and superior lightweight properties.

BACKGROUND ART

In recent years, a radiation-curable resin, for example, a UV-curableresin, has been used in various fields and for various applications.Such types of resins are only cured at a location therein, whichlocation is irradiated by at least a certain amount of radiation. On theother hand, radiation, for example, UV light, attenuates in the processof traveling into a resin. Therefore, it is difficult for radiation toreach deeper levels. In addition, radiation would be absorbed by asubstance absorbent at the same wavelength as that of the radiation.Thus, radiation is greatly subject to attenuation and absorption.

Therefore, a photocurable resin is cured only to a depth of severalmicrometers to several millimeters. That is, the resin is not cured atdeeper levels. Therefore, it is difficult or impossible to apply suchresin as a thick material. In addition, if such resin contains a filler,etc., having a characteristic of hindering the transmission ofradiation, the curing process would be easily disrupted or even blocked.Therefore, the range of applications has been centered on the fields ofphotoresists, coatings, paints, adhesives, varnishes, etc. These are theproblems of such resins.

In order to solve the above problems, a range of products, representedby the following, has been provided:

An easily curable UV-curable resin (that is, an “active radiationcurable composition” from Mitsubishi Rayon Co. Ltd. (see Patent Document1 (JP 8-283388A))); and

A UV-ray-heat curable resin (that is, “Optomer KS series” from AsahiDenka Co. Ltd.; “Radecure” from Hitachi Kasei Kogyo Co. Ltd.; and “UEresin” from Toyo Boseki Co. Ltd. (see Patent Document 2 (JP 61-38023A),etc.)).

However, an easily curable UV-curable resin is subject to interruptionof the curing process when radiation is blocked by a filler, etc. Thisis a problem that is yet to be solved. A UV-ray-heat curable resin isfirst irradiated by UV rays and is then heated. The curability byradiation of such a resin is merely as high as that of photocurableresin. That is, the problems with curing of a thick material or withcuring of a resin containing a filler are not at all solved. Theseproblems are merely addressed by the thermal curing process to becarried out after the photocuring process (this process is able to cureonly a surface layer). That is, these problems have hitherto not beensubstantially solved.

If a technique is established to quickly cure a thick resin materialthat contains a radiation blocking substance and has a characteristic ofattenuating and absorbing radiation to a large degree, this enables suchresin material to be applied not only to the conventional fields ofapplications but also to various other fields to which such resinmaterial has hitherto been not applicable due to the above problems withphotocurable resin. In particular, one such field is that of FRP resins,in particular, CFRP resins.

Conventionally, an FRP lends itself to various processing methods orvarious manufacturing methods. However, a matrix resin is a thermalcurable resin or a thermoplastic resin in most cases. Molding an FRP, inparticular, a CFRP, has the following problems, among others. One isthat temperature control is complicated and therefore prolongs curingtime, resulting in high-cost processing. Another is that curing of alarge FRP material requires a large heating furnace. Yet another is thata resin that is curable within a small amount of time at a normaltemperature cannot be used for a large FRP material that requiresprolonged molding time. Yet another is that change in resin viscositydue to change in temperature changes the stage of resin impregnation,which makes it difficult to carry out the molding process. Yet anotheris that the residual solvent causes generation of voids during theprocess of resin curing, resulting in deteriorated quality of theresultant molded product.

Recently, as a solution to the above problems, application of aphotocurable resin to a matrix has attracted attention. Such a method ofcuring a matrix resin may be represented, in particular, by a filamentwinding method from Loctite Corp., the method using a UV curing processand a thermal curing process together (“fiber/resin compositions and amethod of preparing same” from Loctite Corp. (see Patent Document 3 (JP7-507836A)). However, an FRP molding method using such a composition isproblematically executed as follows. First, an FRP is impregnated withresin but is not yet cured. Subsequently, the FRP is irradiated with UVradiation. This causes the surface thereof to be cured. This also causesthe interior thereof to be gelled to a large degree. This makes itpossible to maintain the shape thereof and the impregnation statethereof to a certain degree. Finally, the curing process is completed byheating.

In this method, very little change in resin viscosity is admittedlycaused by change in temperature. In addition, the handling operationafter the impregnation process is easy to perform. However, the thermalcuring process is necessary for a complete curing. This increases thefuel and light expenses necessary for the thermal curing. This alsorequires prolonged working time. These, along with other factors,contribute to increases in costs of processing. In addition, completionof the curing process requires a prolonged time. In addition, a largeFRP material requires a large heating furnace. These problems, amongothers, are yet to be solved.

In view of the disadvantages of the conventional radiation-curable resinand of an FRP, in particular, a CFRP, the present inventors have studieda technique to cure a thick resin material, containing an radiationblocking substance, by irradiating it, and a technique to radiation curean FRP, in particular, a CFRP. As a result, the present inventors havedeveloped a novel technique regarding a resin composition of the chaincuring type. This technique involves a novel resin curing method able toalso radiation-cure a substance having a characteristic of blockingradiation to a relatively large degree. Such a substance is, forexample, a carbon, a carbon fiber (CF), a metal, a resin containing aninorganic filler, etc., (such as carbon fiber reinforced plastics(CFRP), a carbon/metal/inorganic substance containing resin, etc.). Thistechnique also involves a composition used by the method, a moldedarticle produced by the method, and a molding method based on themethod. See Patent Document 4 (JP 11-193322A) and Patent Document 5 (JP2001-89639A).

The following is the list of the patent documents:

-   Patent Document 1: JP 8-283388A-   Patent Document 2: JP 61-38023A-   Patent Document 3: JP 7-507836A-   Patent Document 4: JP 11-193322A-   Patent Document 5: JP 2001-89639A

SUMMARY OF THE INVENTION Problems to be Solved by the Present Invention

However, as it turned out, a case arose in which, even when such a resincomposition was used, increase in the fiber volume content Vf of a FRPbody to be molded suppressed the chain curing process. In view of this,in JP 2005-216690A, the present inventors provided the inventionrelating to the following RTM molding method. It is noted that thisinvention was not well known at the time of filing of the presentApplication and therefore does not constitute a prior technique withrespect to the present invention.

The above-noted invention relates to the following method. A fiberreinforced material is disposed in a mold. In addition, a resininjection line and a suction line are provided. Both lines are designedto communicate with the interior of the mold. Then, the inner pressureof the mold is reduced via a suction operation. At the same time, aresin composition is injected into the mold. The fiber reinforcedmaterial is thereby impregnated with the resin composition. This methodhas the following features (1) to (3). (1) The above resin compositionis a resin composition of the chain curing type. (2) After the onset ofthe curing reaction in the CCP, the maximum temperature at the front endportion of the chain-cured area within the CCP within 10 seconds fromthe onset is increased by 50 degrees Celsius or more from thetemperature of the resin composition after the completion of theimpregnation process and before the onset of the curing reaction. (3)The resin composition is chain-cured with a fiber volume content Vf ofno less than 41%.

The above-noted invention relates also to the following method. A fiberreinforced material is disposed in a mold. In addition, a resininjection line and a suction line are provided. Both lines are designedto communicate with the interior of the mold. Then, the inner pressureof the mold is reduced via a suction operation. At the same time, aresin composition is injected into the mold. The fiber reinforcedmaterial is thereby impregnated with the resin composition. This methodhas the following features (1) to (3). (1) The above resin compositionis a resin composition of the chain curing type. (2) After the onset ofthe curing reaction in the CCP, the maximum temperature at the front endportion of the chain-cured area within the CCP within 10 seconds fromthe onset is increased so as to reach a temperature no less than thetemperature at the onset of the heat curing reaction in the resincomposition. (3) The resin composition is chain-cured with a fibervolume content Vf of no less than 41%.

The RTM molding method according to the above-described invention hasthe following advantageous effects, among others.

(1) A resin reservoir is provided in a mold. The resin reservoir servesto retain the resin composition. Curing the resin composition in thereservoir enables the temperature of the resin composition immediatelyafter the completion of the curing process of the resin composition tobe increased.

(2) A radiation irradiation window is provided in the injection linerand/or the suction line. The resin composition is irradiated byradiation via the window. This initiates the chain curing reaction inthe resin composition. In addition, the resin composition retained inthe reservoir is chain-cured. This enables the temperature of the resincomposition immediately after the completion of the curing process ofthe resin composition to be increased. Furthermore, as the above fiberreinforced material, a carbon fiber may be adopted. Then, electricallyheating the carbon fiber enables the temperature of the resincomposition immediately after the completion of the curing process ofthe resin composition to be increased.

However, the above-noted invention, although it has distinctlyadvantageous effects as noted above, has the following problems to besolved.

The above-described invention is designed to simply and directly applythe CCP (resin composition of chain curing type) to the RTM (resintransfer molding). Therefore, if a FRP body to be molded is large, andif the fiber volume content Vf of the FRP is large, a case may arise inwhich a carbon fiber must be electrically heated or in which it isdifficult to maintain the resin in a well impregnated state. As such, ithas been desired that a high fiber volume content Vf not constrain thechain curability. In addition, good resin impregnability has also beendesired.

In view of the above, an object of the present invention is to provide aRTM molding device and a RTM molding method designed to make it possibleto obtain a molded body having a superior strength and superiorlightweight properties as well as a stable quality.

Means for Solving the Problem

According to the present invention, the above object is achieved by anRTM molding device comprising:

-   -   a mold having a molded body made of a reinforcement fiber        material disposed therein;    -   a resin injection line communicating to the interior of the        mold;    -   a suction line configured to decrease the inner pressure of the        mold;    -   wherein a resin composition is injected into the mold to        impregnate the body therewith so as to obtain a FRP molded body;    -   wherein the resin composition is a CCP;    -   a CCP accommodating layer containing the CCP and being disposed        adjacent to the outer side of the body;    -   heat conduction suppressing means disposed between the layer and        the mold and serving to suppress conduction of heat from one        side having the layer located thereon to the other side having        the mold located thereon;    -   means for separating the body disposed between the body and the        layer;    -   wherein the layer and the suppressing means are combined so as        to be provided with a Vf limit value defined by the curing        characteristics of the CCP and the characteristics of        dissipation of heat from the CCP into the exterior.

The RTM molding device according to the present invention is preferablyprovided with the following features recited in (1) to (5):

(1) The RTM molding device further comprises a mold layer body composedof means for separating the molded body, the CCP accommodating layer,and heat conduction suppressing means, these three elements layered oneon another; and

-   -   a resin reservoir provided in the mold configured to incorporate        the mold layer body.

(2) The CCP accommodating layer comprises a CCP jacket to be filled withthe CCP introduced from the resin injection line, the CCP jacketdisposed on one side of the molded body or on each of both sides of themolded body.

(3) The heat conduction suppressing means comprises a heat insulatingmaterial having a heat conductivity of 0.3 W/m*K or less.

(4) A surface of the CCP jacket, the surface located toward the moldedbody, is porous.

(5) The CCP jacket and the molded body have a porous plate incorporatinga wire mesh.

Another aspect of the present invention provides a RTM molding devicecomprising:

-   -   a mold having a molded body made of a reinforcement fiber        material disposed therein;    -   a resin injection line communicating to the interior of the        mold;    -   a suction line configured to decrease the inner pressure of the        mold;    -   wherein a resin composition is injected into the mold to        impregnate the body therewith so as to obtain a FRP molded body;    -   wherein the resin composition is a CCP;    -   a CCP jacket configured to incorporate the molded body and        designed to be filled with the CCP introduced from the resin        injection line and disposed on one side of the molded body or on        each of both sides of the molded body;    -   heat conduction suppressing means disposed between the layer and        the mold and serving to suppress conduction of heat from one        side having the layer located thereon to the other side having        the mold located thereon;    -   means for separating the molded body disposed between the molded        body and the layer;    -   wherein the means for separating the molded body, the CCP        accommodating layer, and the heat conduction suppressing means        are layered one on another to compose a mold layer body which is        designed to extend in the longitudinal direction of the molded        body;    -   wherein one side of the mold layer body, the side having a CCP        inlet located thereon, is connected to the resin injection line;    -   wherein the other side of the mold layer body is connected to        the suction line; and    -   wherein the layer and the suppressing means are combined so as        to be provided with a Vf limit value defined by the curing        characteristics of the CCP and the characteristics of        dissipation of heat from the CCP into the exterior.

Yet another aspect of the present invention provides an RTM moldingmethod of molding a molded body by the use of the RTM molding deviceaccording to the present invention.

Yet another aspect of the present invention provides a molded bodymolded by the use of the RTM method according to the present invention.

Advantageous Effects of the Invention

The present invention provides a RTM molding device and a RTM moldingmethod designed to make it possible to obtain a molded body having asuperior strength and superior lightweight properties as well as astable quality.

The present invention makes it possible to constantly maintain the fibervolume content Vf at a proper value while impregnating the molded bodywith the CCP and curing it. This advantageous effect is produced by thefollowing configuration. A CCP accommodating layer is disposed. Thelayer contains the CCP. The layer is disposed adjacent to one side ofthe molded body or to each of both sides of the molded body. A heatconduction suppressing means is disposed. The means is disposed betweenthe layer located on one side or each of both side of the body and themold. This allows the fiber volume content Vf to be maintained at aconstant value or more. The layer and the suppressing means are combinedso as to be provided with a Vf limit value. The value is defined by thecuring characteristics of the CCP and the characteristics of dissipationof heat from the CCP into the exterior.

According to a preferable embodiment of the present invention, a CCP isinjected in a desired supply pattern from the resin injection line 8into the CCP accommodating layer, the layer containing the CCP, thelayer disposed adjacent to one side of the molded body or to each ofboth sides of the molded body. In addition, at the termination portion(located away from the inlet) of the CCP accommodating layer, thesuction line sucks the interior of the CCP accommodating layer (CCPjacket). This causes the CCP from within the CCP accommodating layer tobe impregnated into the molded body via the resin jacket or the porousplate. On the other hand, the heat conduction suppressing means (a heatinsulating material such as wood, etc.) disposed on each of both sidesof the CCP accommodating layer (CCP jacket) suppresses conduction ofheat from the CCP accommodating layer (CCP jacket) into the mold,thereby preventing the temperature of the molded body over the entirelength thereof from decreasing. In addition, the injection amount of theCCP and the heat conduction capacity of the heat conduction suppressingmeans are adjusted in order to prevent the temperature of the moldedbody from excessively increasing. Under these conditions, the moldedbody containing the CCP form the CCP accommodating layer can be cured(chain-cured).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic diagram of an RTM molding deviceaccording to one embodiment of the present invention. The diagramincludes a longitudinal cross sectional view of a molded body.

FIG. 2 is a longitudinal cross sectional view taken along the line A-Ain FIG. 1.

FIGS. 3( a) and (b) are a plan view and a cross sectional view,respectively, illustrating a CCP jacket.

-   -   1: mold    -   1 a: upper mold half    -   1 b: lower mold half    -   3: CCP (resin composition of chain curing type) jacket    -   4: heat insulating body (heat conduction suppressing means)    -   5: molded body (reinforcement fiber material)    -   7: mold releasing sheet    -   8: resin inlet line    -   8 a, 11: on-off valve    -   9: suction line    -   12: radiation transmission window    -   13: aluminum block    -   14: resin reservoir    -   15: pressure container    -   15 a: suction opening    -   16: resin tank    -   17: temperature sensor    -   20: controlling device    -   21: resin flow meter    -   28: perforated plate    -   30: mold layer body    -   30 a: upper horizontal portion    -   30 b: vertical portion    -   30 c: lower horizontal portion

DETAILED DESCRIPTION OF THE INVENTION

The RTM molding device and the RTM molding method according to thepresent invention will be described below in detail based on embodimentsthereof with reference to the accompanying drawings.

FIG. 1 is an overall schematic diagram including a cross sectional viewtaken along the width direction of a molded body in a RTM molding deviceaccording to one embodiment of the present invention. That is, themolded body is configured to extend in a direction perpendicular to theplane of the paper containing FIG. 1. FIG. 2 is a cross sectional viewtaken along the line A-A in FIG. 1. FIG. 2 is a partial cross sectionalview of a molded body. The body is divided in a direction perpendicularto the longitudinal direction of the body. The upper part and the lowerpart of the body are removed. Thus, in FIG. 2, the vertical direction(denoted by an arrow L in the figure) is the longitudinal direction ofthe molded body.

In FIGS. 1 and 2, a mold to be used as a base is composed of an uppermold half 1 a and a lower mold half 1 b. The upper mold half 1 a and thelower mold half 1 b have a mold layer body 30 clamped therebetween. Thebody 30 will be described in detail later. Reference numeral 6 denotes asealing material. Reference numeral 6 is indicated at two locations. Thesealing material 6 seals a mating surface between the upper mold half 1a and the lower mold half 1 b. The longitudinal direction of the moldedbody corresponds to the vertical direction denoted by an arrow L in FIG.2. Actually, the upper mold half 1 a should have been referred to as aright mold half. Likewise, the lower mold half 1 b should have beenreferred to as a left mold half. However, such terms are not usual inthe field of molds. Therefore, the terms “upper mold half” and “lowermold half” are used herein throughout.

A resin reservoir 14 (not shown) is provided in the upper part of themold 1 (that is, the upper part as seen in the longitudinal direction ofthe molded body). In addition, this reservoir 14 is located in the upperend of the mold layer body 30. In addition, this reservoir is locatedtoward the suction line 9. The resin reservoir doubles as a suctionspace.

A resin inlet 14 a is provided at the lower end of the mold. The inlet14 a is connected with the resin inlet line 8. The line 8 is formed froma tube made of copper (however, another appropriate material may also beused). Another resin reservoir (not shown) is provided in the lower endof the body 30. In addition, this resin reservoir is located toward theresin inlet line 8. The resin reservoir serves to enable resin to beinjected into the lower end of the body 30. That is, the resin reservoirserves to prevent the upper mold half 1 a and the lower mold half 1 bfrom preventing resin from being injected into the lower end of the body30.

The resin inlet line 8 is connected to a resin tank 16. The tank 16 isdisposed in a pressure container 15. The line 8 is provided with anon-off valve 8 a. The valve 8 a serves to open and close the line 8.

This embodiment is configured to pressurize the interior of thecontainer 15 when injecting resin. However, this embodiment may bemodified so as to inject resin from the resin tank via a resin injectionpump.

Reference numeral 9 denotes a suction line, as noted above. The line 9is made of copper (however, another appropriate material may also beused). The line 9 is connected to a vacuum pump (not shown). The line 9communicates via the suction opening 15 a to the resin reservoir(suction space) noted above. Reference numeral 11 denotes an on-offvalve. The valve 11 serves to open and close the line 9.

The line 9 is provided with an aluminum block 13. The block 13 has awindow 12 defined therein. The window 12 transmits radiationtherethrough. The block 13 is formed to be generally cubic. The window12 has a glass fitted therein. The block 13 has still another resinreservoir defined therein.

The block 13 may be made of a material other than aluminum. However, thematerial must be such that the resin reservoir can be formed. Inaddition, the material must be such that the radiation transmissionwindow 12 can be provided.

The block 13 may be provided in the resin inlet line 8.

The whole structure extending from the pressure container 15 to theon-off valve 11 is sealed.

The mold layer body 30 is composed of a first horizontal portion 30 a, asecond horizontal portion 30 c, and a vertical portion 30 b. This isshown in FIG. 1. The body 30 is generally Z-shaped as seen in the widthdirection.

FIG. 2 is a longitudinal cross sectional view of the body 30. Referencenumeral 5 denotes a molded body. The body 5 is tabular. The body 5 ismade of, for example, a reinforcement fiber material. Such material isformed by placing woven fabrics each made of a reinforcement fiber oneon another. Such reinforcement fiber is, for example, glass fiber,carbon fiber, aramid fiber, etc.

Reference numeral 3, indicated at two locations, each denotes a chaincuring polymer (CCP) jacket. One of the jackets 3 is located adjacent toone outer side of the body 5. The other of the jackets 3 is locatedadjacent to the other outer side of the body 5. The jacket 3 is filledwith a CCP. This is a resin composition of chain curing type. Thecomposition is injected from the resin inlet line 8.

The CCP jacket 3 may be configured in various ways with various members.However, any configuration must be able to contain a large amount ofresin, as noted above.

FIGS. 3( a) and 3(b) show one such configuration. FIG. 3( a) is a planview of such a jacket 3. FIG. 3( a) is a conceptual diagram. FIG. 3( b)is a cross sectional view of the jacket 3 taken along the line B-B inFIG. 3( a).

The jacket 3 is composed of a longitudinal wall 301, an upper surfacefilm 302, and a lower surface film 303. The wall 301 extends in thedirection in which resin, after being injected, flows. The jacket 3includes a plurality of adjacent grooves.

The CCP jacket 3 may be formed from materials referred to as “corrugatedplastic fiberboard” or “hollow sheet” (available, for example, under thetrade name “twin panel” (Ube-Nitto Kasei Co., Ltd.). These materials aremade of polycarbonate. In addition, these materials are tabular. Thesematerials each have the same cross sectional structure as that of afiberboard. It is clearly more preferable that the jacket be morepreferably made of a material that is heat resistant and stiff to a highdegree, such as wood, ceramic, metal, etc. That is, the jacket 3 may bemade of any of materials of various types, such as: hollow platematerials having the same cross section as that of a fiberboard;honeycomb-structured materials; mesh materials (for example, the resinmeshes, wire meshes, etc.); and various types of corrugated platematerials.

FIGS. 3( a) and (b) are merely conceptual depictions. That is, the CCPjacket 3 may be designed such that the grooves thereof correspond to themolded body in terms of shape. For example, if the body 5 is arcuate inshape, the grooves are adapted to extend along the curve.

The jacket 3 is preferably made of a material having the same crosssection as that of any of various types of corrugated plate materialsand hollow plate materials. In the case of a hollow plate material, thegrooves may be used as a passage to have a measurement instrument, etc,such as a thermocouple, disposed therein.

One of the upper surface film 302 and the lower surface film 303 facesthe body 5. This film has fine pores 304 defined therein. The pores 304are configured to penetrate through the film. The pores 304 each have adiameter of approximately 1 to 2 mm. The pores 304 are disposed alongthe grooves. Each pair of adjacent pores 304 are spaced apart from eachother by a distance of approximately 1 to 2 cm.

The thickness of the CCP jacket is determined from an optimal value ofthe fiber volume content Vf. The fiber volume content Vf is based on thecuring characteristics of the CCP and the characteristics of radiationof heat into the outside. The thickness is mostly approximately 0.5 mmto 20 mm. It is preferably 1 mm to 10 mm. It is more preferably 2 mm to6 mm. If the thickness is less than 0.5 mm, this makes it difficult toinstall the jacket. In addition, this increases to a large degree theamount of heat emitted into the environment. If the thickness is greaterthan 20 mm, this increases to a large degree the amount of unused resinmaterial. This in turn is likely to increase the cost.

As shown in FIG. 2, the body 5 and each of the jackets 3 have a moldreleasing sheet 7 interposed therebetween, respectively. Each of thesheets 7 is placed on the body 5. The sheet 7 is made of a 3TLL, a peelply, etc. The sheet 7 serves to separate the body 5 and the jacket 3from each other.

The outer side of the sheet 7 has a porous plate 28 disposed thereon.The plate 28 is made of a perforated metal, a wire mesh, etc.

The outer side of one of the jackets 3 faces the upper mold half 1 a.The outer side of the other of the jackets 3 faces the lower mold half 1b. Both outer sides and the mold halves 1 a and 1 b have a heatinsulating material 4 interposed therebetween, respectively. The heatinsulating material 4 constitutes a heat conduction suppressing means.This means serves to suppress conduction of heat from the jackets 3 tothe mold halves 1 a and 1 b. In addition, both outer sides and the heatinsulating materials 4 have a Teflon sheet 90 interposed therebetween,respectively. The term “Teflon” is a registered trademark.

The heat insulating material 4 serves to enhance the chain curingreaction in the resin. Therefore, the material 4 is preferably made ofwood. The reason is that wood is low in cost and has high heatinsulation characteristics. However, as is described below, thetemperature of the molded body 5 is controlled. Therefore, a materialhaving varied heat conductivity may be adopted.

That is, the heat insulating material 4 has a heat conductivity of 0.3W/(m*K) or less. It is preferably 0.2 W/(m*K) or less. It is morepreferably 0.1 W/(m*K) or less. Such heat insulating material is, forexample, wood, heat insulating board, etc.

In the present invention, a heat conduction suppressing means using thejacket 3 and the heat insulating material 4 is designed to make itpossible to cure a CCP at a fiber volume content Vf no greater than alimit value. The content Vf is a volume content of fibers in a moldedbody, which is made of fiber reinforced plastics (FRP). The limit valueof the content Vf is determined from the curing characteristics(described later) of the CCP and the characteristics of radiation ofheat from the jacket 3 into the outside via the heat conductionsuppressing means using the heat insulating means. For example, if a CCPis intended to be curable at a content Vf no greater than 43%, the meansis designed to make it possible to sufficiently cure the CCP at anycontent of Vf not less than 43%.

A CCP is a resin composition of the chain curing type, as noted above. ACCP is adopted for the RTM molding device according to the presentinvention. Such a CCP is a matrix resin to be filled into the CCP jacket3. The CCP begins to cure upon exposure to radiation, such as UVradiation, etc. During the curing process, the CCP utilizes the heatarising from the curing reaction thereof to induce a chain curingreaction.

That is, in the above CCP, upon exposure to radiation, the locationexposed to radiation begins to cure. Subsequently, the heat arising fromthis curing reaction induces a chain curing reaction at the location.Therefore, the curing process can be completed whether or not radiationpenetrates to places other than the surface of the CCP, and whether ornot the radiation is blocked by obstacles and is thereby prevented frompenetrating to places other than the surface of the CCP. Therefore, theCCP is quickly cured even at deeper levels. For example, a carbon fiberreinforced plastic (CFRP) that is 1 cm thick can be completely curedwithin three minutes.

Such a CCP may be a resin composition disclosed in JP 11-193322A. Thiscomposition comprises, in a specific weight ratio: a component acting asa photo/thermal initiator of cationic polymerization; and aphotoinitiator for cationic polymerization. In this resin composition, aCFRP that is 1 cm thick is curable within three minutes.

A superior resin composition disclosed in JP 11-193322A comprises 100parts by weight of a photopolymerizable resin; and 0.6 to 5 parts byweight of a component acting as a photopolymerization initiator composedof at least two components. The photopolymerizable resin is selectedfrom a group consisting of: a photopolymerizable epoxy polymer, such asan alicyclic epoxy, a glycidyl ether epoxy, an epoxidized polyolefin,etc.; and a vinyl ether compound. A superior resin compositioncomprises, in a weight ratio of 1 to 4: a component acting as aphoto/thermal initiator of cationic polymerization; and a photoinitiatorfor cationic polymerization.

A photo/thermal initiator of polymerization may initiate polymerizationby one or both of light and heat (see JP 7-300504A, section [0002]).

Alternatively, a resin composition of the chain curing type disclosed inJP 2001-89639A may also be adopted. This resin composition of the chaincuring type uses an iron-allene compound as a specificphotopolymerization initiator. In addition, this resin compositioncomprises, in a ratio: 1 mole of a photo-polymerizable resin able toreact with a component acting as a curing agent; and 0.1 to 1.4 moles ofthe component acting as a curing agent. All this together is able toinduce a chain curing reaction in the resin composition. Alternatively,a specific sulfonium salt is used. In addition, this resin compositioncomprises: 1 mole of a photopolymerizable resin able to react with acomponent acting as a curing agent; and 0.1 to 1.4 moles of thecomponent acting as a curing agent. In addition, this resin compositioncomprises: 100 parts by weight of all components except the componentacting as a photopolymerization initiator; and 0.1 to 6.0 parts byweight of the component acting as a photopolymerization initiator. Allthis together induces a chain curing reaction in the resin compositionupon exposure to UV light (ultraviolet light).

Alternatively, a resin compound from Elementis Co., Ltd., disclosed inU.S. Pat. No. 6,245,827 B1 may be adopted. This resin compositioncomprises, as a photopolymerizable resin, an alicyclic epoxy, a vinylether or a mixture of one of these and an epoxidized polyolefin. Inaddition, this resin composition comprises at least one thermalpolymerization initiator made of organic peroxide and one photo/thermalinitiator of cationic polymerization added thereto. In addition, thisresin composition comprises an α-hydroxyketone as a sensitizing agent.All this together is able to induce likewise a chain curing reaction inthis resin composition.

Another matrix resin is, for example, another resin composition made byElementis Co. Ltd. This resin composition induces the same mechanism ofchain curing as described above. This resin composition is, for example:a vinyl ether resin composition; a glycidol containing resincomposition; an oxetane resin composition, or a radical composition.

In FIG. 1, reference numeral 17 indicated at plural locations denotes atemperature sensor composed of a thermocouple, etc. The sensors 17 arespaced apart from each other by a predetermined distance (for example,approximately 4 cm). The sensors 17 are disposed on the molded body 5.Alternatively, the sensors 17 are disposed on the jackets 3 and areproximal to the body 5. The sensors 17 are arranged sequentially fromthe inlet side connected to the resin inlet line 8 to the side opposedto the inlet side and connected to the suction line 9. Thus, the sensors17 serve to measure the temperature of the body 5.

Reference numeral 21 denotes a resin flow meter. The meter 21 isdisposed in the line 8. The meter serves to measure the flow of a CCPinjected into the jackets 3.

Reference numeral 20 denotes a control means. The means 20 receives asignal representing the temperature of the body 5 measured by each ofthe sensors 17. The means 20 also receives a signal representing theflow of the injected CCP measured by the meter 21. This is performed foreach product to be molded. This makes it possible to maintain consistentquality. The means 20 performs a control operation based on the measuredflow of the injected CCP in order to ensure that an appropriate flow ofa CCP is injected into the jackets 3.

In the RTM molding device configured as described above, the mold layerbody 30 accommodating the molded body 5 is between the upper mold half 1a and the lower mold half 1 b. Then, the sealing material 6 sealsfluid-tightly a mating surface between the upper mold half 1 a and thelower mold half 1 b.

Subsequently, the CCP, after being degassed, is placed in the resin tankin the pressure container. Subsequently, the on-off valve 8 a in theresin inlet line 8 is closed. Subsequently, the line section runningfrom the pressure container 15 to the valve 8 a is gradually evacuated(that is, the inner pressure thereof is decreased to a sufficiently lowpressure). Subsequently, the on-off valve 11 is opened. Subsequently,the vacuum pump (not shown) is caused to evacuate the suction line 9.This causes the mold 1 to be evacuated (that is, the inner pressurethereof is decreased to a sufficiently low pressure). Subsequently, theinterior of the pressure container is pressurized to a normal pressureor several atmospheres. Subsequently, the valve 8 a in the line 8 andthe valve 11 in the line 9 are opened. This causes the CCP (resincomposition of chain curing type) stored in the resin tank 16 in thecontainer 15 to be discharged to enter into the CCP jackets 3 via theline 8. This results in the jackets 3 being filled with the CCP.

The CCP after being filled in the CCP jackets 3 flows through thegrooves described above. Subsequently, the CCP exits the pores 304defined in the film designed to cover the grooves. Subsequently, the CCPpasses through the mold releasing sheets 7 (and through the perforatedplates 28). Subsequently, the CCP permeates the molded body 5. Thisresults in the body 5 being impregnated with the CCP.

This also results in the resin reservoir in the upper end of the moldlayer body 30 having resin stored therein. This also results in thealuminum block 12 having resin stored therein.

When the jackets 3 are completely filled with the CCP, this is confirmedby the measurements of the resin flow, etc. Upon confirming this, theon-off valve 11 is closed. Subsequently, the interior of the pressurecontainer is pressurized to, for example, six atmospheres. Subsequently,resin is injected under pressure. The jackets 3 are thereby betterimpregnated with resin, thereby resulting in voidless impregnation.Then, the vacuum pump (not shown) is stopped. This ends the operation ofimpregnating the CCP into the body 5.

Subsequently, the CCP is cured by being irradiated with radiationentering through the radiation transmission window 12 provided in thealuminum block 13. A UV-curable resin composition is irradiated withultraviolet light. This initiates chain curing of the CCP. Chain curingmay be initiated by various types of radiation. However, it is certainlyalso possible to heat part of the block 13 or part of the copper tube,that is, the line 9.

The block 13 has a resin reservoir formed therein, as noted above. Whencuring is initiated by UV, etc., this will then result in chain curing.This causes resin in the suction line 9 to be sequentially chain-cured.The chain curing reaction proceeds to the resin reservoir 14. Thereservoir 14 accommodates solely CCP. Therefore, the chain curingreaction proceeds quickly through the reservoir 14 and through theZ-shape passage in the Z-shaped mold layer body 30 to the lower end ofthe body 30. That is, the chain reaction proceeds through the wholelength of the Z shape in the direction from the suction line 9 towardthe inlet line 8.

As noted above, there is another resin reservoir provided in the lowerend of the body 30. This reservoir is located toward the inlet line 8.This reservoir may be provided with a thermocouple. It may be therebydesigned such that that when the thermocouple detects the heat generatedby the chain curing reaction, this causes the valve 8 a located towardthe inlet line 8 to be closed. This prevents the remaining resin in thepressure container 15 from being chain-cured. The interior of thepressure container may be pressurized at a pressure of approximately 6atmospheres until the end of the chain curing reaction. In thisembodiment, the process of resin impregnation can be performedthroughout in an excellent manner by the thermocouple monitoring theresin reservoir located toward the inlet line 8 and by pressurizing theinterior of the mold layer body 30 until immediately before the end ofthe chain curing reaction.

After the onset of the curing reaction in the CCP, the maximumtemperature at the front end portion of the chain-cured area within theCCP within 10 seconds, preferably 5 seconds, most preferably 3 seconds,from the onset of the curing reaction is increased by 50 degrees Celsiusor more from the temperature of the resin composition after thecompletion of the impregnation process and before the onset of thecuring reaction. The inventors confirmed that the temperature differenceof 50 degrees Celsius or more causes the chain curing reaction toproceed. The temperature difference is preferably 70 degrees Celsius ormore, more preferably 100 degrees Celsius or more. When such atemperature difference is maintained, this makes it possible to maintainthe resin characteristics (for example, the resin viscosity) that arepreferable for the molding operations, such as resin injection, that areto be performed before the onset of the curing reaction, over the entiretime necessary for executing such operations.

The positive temperature gradient at the front end portion of the curedarea within the CCP during the chain curing process is 300 degreesCelsius per minute or more, more preferably 600 degrees per minute ormore, most preferably 1000 degrees Celsius per minute or more.

The above advantageous effect can be obtained by the followingalternative procedure. After the onset of the curing reaction in theCCP, the maximum temperature at the front end portion of the chain-curedarea within the CCP within 10 seconds from the onset, preferably 5seconds, most preferably 3 seconds, from the onset of the curingreaction is increased so as to reach a temperature no less than thetemperature at the onset of the heat curing reaction in the resincomposition. In addition to the temperature at the onset of the heatcuring reaction, it is preferable to reach a temperature of no less than20 degrees Celsius. Furthermore, in addition to the temperature at theonset of the heat curing reaction, it is more preferable to reach atemperature of no less than 50 degrees Celsius. The temperature at theonset of the heat curing reaction is defined by the temperature at theonset of the heat curing reaction (onset value) and the temperature atthe end of the heat curing reaction (end value), both measured by thedifferential scanning calorimeter (DSC) (the rate of temperatureincrease is 10 degrees Celsius per minute).

If carbon fiber is adopted as a reinforcement fiber material for theCCP, and if the fiber volume content Vf reaches a value not less than41%, even a resin composition of the chain curing type is difficult tosufficiently cure. In this embodiment, the resin reservoir 14 and theresin jacket 3 together make it possible to maintain the conditions thatallow the chain curing reaction to proceed uninterrupted.

In the molding device according to the present invention, a fiber volumecontent Vf of 41 to 70% is sufficient to enable the chain curingreaction to proceed uninterrupted.

The RTM molding device according to this embodiment of the presentinvention is configured as described above. This embodiment includes thefollowing configuration. The upper mold half 1 a and the lower mold half1 b have a molded body 5 disposed therein. The body 5 is made of areinforcement fiber material. The CCP jackets 3 are disposed along thelongitudinal direction of the body 5. The jackets 3 are disposedadjacent to both outer sides of the body 5, respectively. The jacket 3is filled with a CCP (resin composition of the chain curing type). Theouter side of one of the jackets 3 faces the upper mold half 1 a. Theouter side of the other of the jackets 3 faces the lower mold half 1 b.Both outer sides and the mold halves 1 a and 1 b have a heat insulatingmaterial 4 interposed therebetween, respectively. The heat insulatingmaterial 4 constitutes a heat conduction suppressing means. This meansserves to suppress conduction of heat from the jackets 3 to the moldhalves 1 a and 1 b. In addition, the outer jackets 3 and the body 4 havea porous plate 28 disposed therebetween, respectively. The plate 28 ismade of a perforated metal, a wire mesh, etc.

The above configuration makes it possible to inject a CCP in a desiredsupply pattern from the resin injection line 8 into the jackets 3. Thejackets 3 are disposed along the longitudinal direction of the body 5 onboth outer sides of the body 5, respectively. The above configurationalso makes it possible to impregnate the CCP into the body 5 via theporous plates 28 while the suction line 9 is sucking the CCP from insidethe jackets 3.

The above configuration also makes it possible to appropriatelychain-cure the molded body 5 without occurrence of the following twoevents. The first event involves generating decrease in temperature overthe whole length of the body 5. The second event involves generatingexcessive increase in temperature. The first event is prevented bysuppressing dissipation of heat from the jackets 3 into the mold halves1 a and 1 b by use of the heat conduction suppressing means. This meansis, as noted above, for example, the heat insulating materials 4disposed on both outer sides of the jackets 3, respectively. The secondevent is prevented by appropriately adjusting the heat conductioncapacity of the heat conduction suppressing means.

INDUSTRIAL APPLICABILITY

The present invention relates to a resin transfer molding (RTM) methodand to a resin transfer molding device to be used when molding fiberreinforced plastics (FRPs). In particular, the present inventioninvolves using a chain curing polymer (CCP). This is a resin compositionof the chain curing type. The present invention enhances thereby thefiber volume content of the FRP body to be molded. In addition, thepresent invention thereby makes it possible to obtain a molded bodyhaving superior lightweight properties.

The invention claimed is:
 1. A resin transfer molding (RTM) devicecomprising: a mold having an interior comprising a resin reservoir, themold holding within said interior a molded body made of a reinforcementfiber material and holding at each of opposite surfaces of the moldedbody a hollow chain curing polymer (CCP) accommodating layer having athickness of approximately 0.5 mm to 20 mm, a heat insulating memberpositioned between each CCP accommodating layer and the mold, and aseparating element positioned between the molded body and each CCPaccommodating layer; a resin injection line injecting CCP resin into theresin reservoir and into the remaining interior of the mold toimpregnate the molded body and to fill each CCP accommodating layer; aradiation source initiating curing of said injected resin; and a suctionline decreasing pressure of the interior of the mold, wherein CCP resincuring in the resin reservoir and in each CCP accommodating layergenerates heat maintaining conditions allowing for a chain reaction ofthe injected resin to proceed uninterrupted so as to form afiber-reinforced plastic (FRP) molded body, and wherein the FRP moldedbody has a fiber volume content (Vf) limit value depending on curingcharacteristics of the CCP resin and on heat dissipation characteristicsof the CCP resin to outside of the mold.
 2. The RTM device of claim 1,wherein each separating element and adjacent CCP accommodating layer arelayered on each other to form a mold layer body.
 3. The RTM device ofclaim 1, wherein each CCP accommodating layer comprises a CCP jacket. 4.The RTM device of claim 3, wherein a surface of each CCP jacket locatedon a side adjacent to the molded body is porous.
 5. The RTM device ofclaim 3, wherein a porous plate comprising a wire mesh is positionedbetween each separating element and CCP jacket.
 6. The RTM device ofclaim 1, wherein each CCP accommodating layer has a thickness of 1 mm to10 mm.
 7. The RTM device of claim 1, wherein each CCP accommodatinglayer has a thickness of 2 mm to 6 mm.
 8. The RTM device of claim 1,wherein the FRP molded body has a fiber volume content (Vf) of 41% to70%.
 9. The RTM device of claim 1, wherein the insulating membercomprises a heat insulating material having a heat conductivity of 0.3W/m*K or less.
 10. A resin transfer molding (RTM) device comprising: amold having an interior comprising a resin reservoir, the mold holdingwithin said interior a molded body made of a reinforcement fibermaterial and holding at each of opposite surfaces of the molded body ahollow chain curing polymer (CCP) jacket having a thickness ofapproximately 0.5 mm to 20 mm, a separating element positioned betweenthe molded body and each CCP jacket, and a heat insulating memberpositioned between each CCP jacket and the mold; a resin injection lineinjecting CCP resin into the resin reservoir and into the remaininginterior of the mold to impregnate the molded body and to fill each CCPaccommodating layer; a radiation source initiating curing of saidinjected resin; and a suction line decreasing pressure of the interiorof the mold, wherein CCP resin curing in the resin reservoir and in eachCCP jacket generates heat maintaining conditions allowing for a chaincuring reaction of the injected resin to proceed uninterrupted so as toform a fiber-reinforced plastic (FRP) molded body, wherein eachseparating element, CCP jacket, and the insulating member are layered oneach other to form a mold layer body, wherein the interior of the mold,adjacent to one side of the mold layer body, has a CCP resin inletconnected to the resin injection line, wherein the interior of the mold,adjacent to another side of the mold layer body, is connected to thesuction line, and wherein the FRP molded body has a fiber volume content(Vf) limit value depending on curing characteristics of the CCP resinand on heat dissipation characteristics of the CCP resin to outside ofthe mold.
 11. The RTM device of claim 10, wherein each CCP jacket has athickness of 1 mm to 10 mm.
 12. The RTM device of claim 10, wherein theCCP jacket has a thickness of 2 mm to 6 mm.
 13. The RTM device of claim10, wherein the FRP molded body has a fiber volume content (Vf) of 41%to 70%.
 14. The RTM device of claim 10, wherein the insulating membercomprises a heat insulating material having a heat conductivity of 0.3W/m*K or less.